This invention is generally in the area of drug delivery and gene therapy devices and more specifically in the area of delivery of drugs and gene transfer via polymeric microparticles, including liposomes in a polymeric matrix.
A variety of materials have been developed for delivery of drugs, nucleic acids, and biologics. Examples include microspheres, microcapsules, and microparticles formed of biodegradable or non-biodegradable polymers which release the incorporated material over time or following exposure to specific conditions. Targeting of the materials, other than through direct administration at the targeted site, has been very difficult. Most are administered systemically if multiple release sites are required.
More recently, polymeric gels or films have been utilized for drug delivery and gene therapy, especially of small oligonucleotides such as antisense. Liposomes have also been utilized for delivery of genetic material, with varying degrees of success, primarily due to the inherent instability and short half-lives of the liposomes.
Gene therapy is typically used to refer to delivery of nucleic acid molecules which control expression of a particular endogenous gene, or to delivery and expression of an exogenous gene, which functions in addition to, or in place of, a defective or missing endogenous gene.
Three methodologies have been developed as the principal mechanisms for gene therapy: delivery via cationic lipids, for example, in the form of liposomes or vesicles, molecular conjugates, and recombinant viral vectors. These methods were recently reviewed by Morgan, Ann. Rev. Biochem., 62:191 (1993), Mulligan, Science 260:926 (1993), and Tolstoshev, Ann. Rev. Pharm. Toxicol., 32:573 (1993).
Although the three major groups of gene transduction methodology are relatively efficient, the percentage of targeted cells that can be transduced in vivo remains relatively low. To treat conditions requiring a higher percentage of gene transduction, new technologies for increasing the percentage of transduced cells would be very useful.
Furthermore, it is very difficult to target cells for delivery of genes, other than through local administration or through selection of viral vectors which infect only certain types of cells, such as replicating cells. Local delivery has advantages in that the effective local concentration is much higher than can normally be achieved by systemic administration, while the systemic concentration remains very low, thereby avoiding serious side effects. There are few methods available, however, which allow one to target scattered areas throughout the body, to achieve local release without systemic involvement.
The ability to express recombinant genes in the blood vessel wall has raised prospects for gene therapy of vascular disease. Two general approaches to introducing genes into the vessel wall have been studied. In one approach, referred to as direct gene transfer, target cells are first isolated and gene transfer is accomplished in vitro; cells that express the recombinant gene product are then selected and transplanted into the host vessel wall. In the second approach, genes are delivered “in situ” to cells within the vessel wall; this direct, in vivo approach to delivery of genes is attractive as a therapeutic modality since it mitigates the need to remove vascular cells from the patient. Since direct gene transfer precludes the opportunity to select for positive transfectants, however, it is essential that an adequate amount of DNA be introduced and expressed by the target tissue. Vascular smooth muscle cells may be suitable targets for the direct gene transfer approach because of their proximity to the lumen surface and abundance in the vessel wall.
Furthermore, abnormal accumulation of smooth muscle cells is a feature of atherosclerosis and of certain accelerated forms of vascular disease, such as restenosis following balloon angioplasty.
One potential means of transfecting smooth muscle cells within the vessel wall is through the use of cationic liposomes. Liposome-mediated gene transfer is a convenient method of transferring recombinant DNA into cells and has been used to directly transfect the arterial wall of live animals. The efficiency of successful gene transfer using cationic liposomes, however, is variable and highly dependent on the cell type. Most in vitro experience to date has been with continuous/immortal animal cells lines. The results studied using these types of cells, however, have uncertain implications for the likelihood success of direct arterial gene transfer in patients.
Local delivery of growth factors has been attempted in several ways. Takeshita, et al., J. Clin. Invest., 93:662-670, (1994), delivered a bolus of a transforming vector for the growth factor VEGF to rabbits. Unfortunately, delivery was not limited to a local area. U.S. Pat. No. 5,238,470 Nabel et al discloses administering transforming vectors to arteries via a double-balloon catheter. A major limitation to this method is that the genetic material is administered all at once, resulting in inefficient transduction. A further limitation is that Nabel requires a substantial instillation time, approximately 30 minutes, resulting in prolonged arterial blockage.
There is therefore a need for an improved, specific delivery means for nucleic acid molecules and other drugs, or bioactive molecules.
It is therefore an object of the present invention to provide a method and means for targeted delivery of bioactive molecules, especially nucleic acid molecules, to tissues or cells in a patient.
It is a further object of the present invention to provide a delivery means that protects the bioactive molecules from proteases and nucleases.
It is still a further object of the present invention to provide a means for locally administering bioactive molecules to tissues or cells in a patient in a controlled, sustained manner.